Illustrated Catalogue Of Magic Lanterns (after November 1889, probably 1890)

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36 MCINTOSH BATTERY AND OPTICAL CO., CHICAGO, ILL., IT. 8 . A. THE LECTURER’S ELECTRIC SIGNAL. TheLecturer’s Telegraph or Electric Signal is something that the lecturer must have. He must have some means of communi- cation with his operator. The old methods of communication have been by means of a small bell; or by the disclosing of the colored signal light in the lecturer’s reading lamp; and in some cases if the lecturer uses a pointer, he holds it in a certain position on the screen ; sometimes he taps the floor ; but there are serious objec- tions to all these methods, as they attract the attention of the audience from the lecture, and by apprising them of the change of views frequently mar an otherwise beautiful dissolving effect. This Electric Signal consists of a battery of zinc and carbon elements, the only chemical used is the ordinary sal ammoniac, to which water is added, so that the battery is a perfectly clean one; no disagreeable odor; no acid to slop over and ruin the clothing, very easily kept in order, and very inexpensive, costing less than i cent an hour ; it also has what is called an “Electric Buzzer” and the sound of which can be so regulated as to be